1. Field of the Invention
This invention relates to laminated transparencies and, in particular, to a heatable, laminated windshield wherein air is prevented from diffusing into the interior of the windshield during lamination.
2a. Technical Considerations
It has been known to pass electric current through a transparent conductive coating on a transparency in order to raise its temperature. Generally, the transparency includes a spaced pair of bus bars electrically interconnected by a conductive coating. The bus bars are usually connected by leads to a power source to distribute current from the power source through the coating. Where the transparency is a laminated windshield, passing current through the coating elevates the temperature of the laminate sufficient to melt snow or ice that has accumulated on an exposed surface of the windshield.
A heatable windshield may include a cut-out section, or notch area, along an edge of one of the plies of the windshield that exposes a lead portion of the bus bars and provides a location at which the power source can be connected to the windshield. During lamination, the windshield components are exposed to elevated temperatures and pressures. After lamination, air bubbles have been observed within the windshield in the vicinity of the notch area. It is believed that this defect is the result of air diffusing through the bus bar leads into the interior of the windshield during lamination. Not only is the bubbling a visible and objectionable defect but excessive bubbling within the windshield may reduce the windshield strength in this area and cause delamination.
It would be advantageous to have a windshield that does not have or will not develop bubbles in the interior of the windshield in the vicinity of the notch area.
2b. Patents of Interest
U.S. Pat. Nos. 3,789,191 and 3,789,192 to Spindler teach a heated window with a temperature sensing device, wherein the electrical leads to the temperature sensor are embedded within the plastic interlayer of the window.
U.S. Pat. No. 3,790,752 to Boaz et al. teaches a heatable, laminated windshield in which an electrical connection is made within the windshield to a transparent interlayer which has a conductive coating thereon. The connection is sealed so that moisture cannot penetrate the laminate.
U.S. Pat. Nos. 3,794,809 to Beck; 4,543,466 to Ramus; and 4,786,784 to Nikodem et al. teach an electrically heatable windshield with opposing bus bars that are electrically interconnected by an electroconductive coating on an interior surface of the windshield. In Beck, the leads to the bus bars extend outside of the windshield assembly. In Ramus and Nikodem et al., the leads extend into a cut-out portion, or terminal area, along an edge of the windshield. Electrical power is provided to the leads at the terminal area.
U.S. Pat. No. 4,593,175 to Bowser et al. teaches a coating composition to prevent moisture from penetrating along a power cable of an electrically heated architectural glazing unit.